The present invention relates in general to a controlled-flow lubricating system which continuously and internally pumps a re-circulating filtered liquid lubricant through and across one or more bearings, and in particular through a bearing which supports the arbor shaft of an abrasive cutting saw.
2. Description Of The Prior Art
In many industrial applications, rolling bearings of the anti-friction type are required to support horizontal and vertical rotatable shafts. In practice, no rolling bearing has a pure rolling contact. The total friction in a bearing is made up of rolling friction, partial sliding, and fluid resistance of the lubricant. This total friction varies somewhat with load, method of lubrication, and the quality and amount of lubricant.
Since rolling friction is inherently low, among the anti-friction bearings those which have the lowest friction coefficients include self-aligning ball bearings, cylindrical roller bearings, and thrust ball bearings.
Improper lubrication will cause wear, pitting, smearing, or corrosion in bearings. Overlubrication will produce excess friction and heat.
The speed of a bearing is the most important factor and is usually limited by the temperature rise that occurs within the bearing at high speeds due to friction. Grease is suitable for low-to-medium speeds, while a liquid lubricant, typically oil, is required for higher bearing speeds.
At low-to-medium speeds, bearing rotation creates turbulence and churning which keeps the bearing surfaces covered with an adequate lubricant film to constantly prevent metal-to-metal contact between the bearing's rolling elements and their raceways.
At higher speeds, however, the centrifugal forces have the damaging effect of depriving the innermost bearing surfaces from receiving a sufficient lubricant film, which may cause an excessive temperature rise requiring that internal heat be removed from the bearing's housing.
Even when a bearing is properly lubricated and protected from foreign matter and overloads, it will ultimately fail from normal fatigue, which is evidenced by a spalling or flaking of one of the raceways or occasionally of the surfaces of the rolling elements themselves.
U.S. Pat. No. 2,950,943 describes a typical system for lubricating anti-friction bearings. It includes an oil bath and a slinger rotatably mounted on the bearing's shaft. Upon rotation, the slinger dips into an oil reservoir and splashes oil around by centrifugal force to create an oil mist in the reservoir which is then directed towards the bearing's rolling elements.
It is well known in the bearing art that slinger lubrication is irregular, non-uniform across the bearing's raceways and across rolling elements, and is incapable of generating sufficient pressure in the oil mist for flushing out foreign debris and wear products which frequently accumulate between the rolling elements and the engaging raceways of the bearing.
Forced feed lubricators have also been suggested but they require at least an external oil reservoir, an external oil pump, a filter, an orifice for directing an oil jet into the bearing, and even a scavenger pump for returning the oil to the reservoir for subsequent recirculation through the bearing.
However, when there is some inadequacy in the design of the bearing, poor shaft mounting, improper lubrication, cooling, and/or flushing, then friction rapidly increases inside the bearing to the great detriment of its rolling elements.
The operational environment is also a very important factor to consider, for example, in the art of abrasive cutting, almost any type of material can be cut when the abrasive blade rotates at a relatively high speed and is dynamically balanced.
For example, the bearings supporting the arbor shaft of a concrete cutting saw must be kept at their peak performance to ensure dynamic balance of its cutting blade. Any flutter of the arbor shaft will accelerate the damage inflicted upon the expensive diamond blade.
In dry abrasive cutting, the peripheral speed of the blade is extremely important. For example, a blade running at a surface speed of 15,000 FPM (feet/min) will be about twice as efficient as a blade operating at 9,000 FPM. But to maintain adequate bearing lubrication at such high speeds is very difficult with the present state of the art, especially for bearings supporting vertical shafts.